Biblical prohibitions

Sexual relations with certain close relatives are forbidden in the Hebrew Bible. Though they are generally called incestuous relations, the biblical list does not necessarily correspond to those prohibited under state laws. In the Hebrew Bible, sexual relationships between siblings are forbidden to Jews but permissible to Gentiles (non-Jews).^[4]

The relationships forbidden by Leviticus 18 are:

• One's genetic relative (Leviticus 18:6)^{[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]}
• One's mother (Leviticus 18:7)
• One's father (Leviticus 18:7)
• One's stepmother (Leviticus 18:8)
• One's paternal or maternal sister (Leviticus 18:9)
• One's paternal sister through one's father's wife (Leviticus 18:11)
• One's daughter (inferred from Leviticus 18:10. Talmud Gittin 83a also implies that the prohibition on marrying one's daughter is a matter of Torah law ^[23])
• One's granddaughter (Leviticus 18:10)
• A woman and her daughter (Leviticus 18:17)
• A woman and her granddaughter (Leviticus 18:17)
• One's aunt by blood (Leviticus 18:12–13)
• One's father's brother (uncle) (Leviticus 18:14)
• One's father's brother's wife (aunt) (Leviticus 18:14)
• One's daughter-in-law (Leviticus 18:15)
• One's brother's wife (sister-in-law) (Leviticus 18:16), with the exception of Yibum
• One's wife's sister (sister-in-law) during one's wife's lifetime, even if since divorced (Leviticus 18:18)

Rabbinically prohibited relationships

In addition to the relationships biblically prohibited to Jews, rabbis have gone further to prohibit additional relationships with various blood relatives or in-laws. These are called "Shni'ot" (secondary prohibitions or seconds). Some of these are:^[1]

• One's grandmother
• One's brother
• One's great-grandmother
• One's grandfather's wife
• One's great-grandfather's wife
• One's grandson's wife

Adopted children who are raised together are not permitted to marry because of appearances, even if they are not biologically related.^[24]

Biblical peoples

A Jew is prohibited from marrying a male Moabite and Ammonite convert (Deuteronomy 23:4); or an Egyptian or Edomite convert up to the third generation from conversion (Deuteronomy 23:8–9).

Nethinim/Gibeonites are prohibited by rabbinic injunction.^[25]

As the people currently living in those areas may not be descended from the original peoples, these prohibitions may not apply today.^[26]

Mamzer

A mamzer in Jewish law is a child resulting from an incestuous liaison or an adulterous liaison by a married woman.^[27] (This is not necessarily the same definition as a bastard by other societies, as it does not include a child of an unmarried woman.)^[27] As a mamzer is excluded from the assembly (Deuteronomy 23:3), the Talmud forbids a marriage by an ordinary Jew to a mamzer.^[28] However, a mamzer may marry a convert or another mamzer, though their child would also be considered a mamzer.^[29]

Certain eunuchs

Jewish tradition also forbids marriage to a man who has been forcibly emasculated; the Greek term spadon (σπάδων; Latin: spado) which is used to refer to such people, is used in the Septuagint to denote certain foreign political officials (resembling the meaning of eunuch).^[27] The Jewish prohibition does not include men who were born without visible testicles (conditions including cryptorchidism), or without a visible penis (intersex conditions can affect genital appearance).^[27] There is dispute, even in traditional Judaism, about whether this prohibited group of men should include those who have become, at some point since their birth, emasculated as the result of a disease.^[30]

Orthodox view

Orthodox Judaism interprets (Leviticus 18:22) as forbidding homosexual acts between two men, and calls it an abomination. (Leviticus 18:14 specifically prohibits such relationships with one's father or uncle.)^[33]

There is no punishment prescribed in the Torah for sex acts between two women (lesbianism), but rabbinic law has prohibited it as an extension of the "activities of (ancient) Egypt" (see Leviticus 18:3).^[34] Although the practice is not considered adultery in the formal sense, the Talmud (Yevamot 76a), in the name of Rav Huna, suggests that women engaged in such practices are forbidden to marry a priest of Aaron's lineage. Others posit that such relationships do not prohibit the woman unto a kohen, since it is merely an act of lewdness.^[35] However, such practices are still censured and are said to be an infringement of the prohibition, "You shall not do as they do in the land of Egypt" (Leviticus 18:3).^[36]

Conservative view

Conservative Judaism's Committee on Jewish Law and Standards has validated different approaches to homosexual acts, with one opinion being like the Orthodox position in many respects, and another opinion permitting many forms of homosexual sex, while continuing to regard anal intercourse between men as prohibited.

In 2012, the American branch of Conservative Judaism represented by the Rabbinical Assembly, devised a commitment ceremony for same-sex couples, though not defined as kiddushin.^[37][38] In 2014, the British group Masorti Judaism said it would support shutafut ceremonies for same-sex unions.^[39][40] In 2016, the Rabbinical Assembly passed a resolution supporting transgender rights.^[41][42]

Humanistic Judaism

In 2004, the Society for Humanistic Judaism issued a resolution supporting "the legal recognition of marriage and divorce between adults of the same sex", and affirming "the value of marriage between any two committed adults with the sense of obligations, responsibilities, and consequences thereof".^[43]

Reform view

Reform Judaism interprets Leviticus 18:22 as forbidding men from using sex as a form of ownership over men. Reform Jewish authors have revisited the Leviticus text, and ask why the text mentions that one should not lie with a man "as with a woman". If it is to be assumed that the Torah does not waste words, the authors ask why the Torah includes this extra clause. Most Reform Jews suggest that since intercourse involved possession (one of the ways in which a man "acquired" a wife was to have intercourse with her), similar to the Christian theology of using sex to "consummate" a marriage, it was abhorrent that a man might acquire another man—it is not the act of homosexual intercourse itself which is abhorrent, but using this act to acquire another man and therefore confuse the gender boundary.^[44]

Ability to give consent

Children, however, were not regarded as old enough to make an informed decision, and so could not consent to marriage themselves,^[27] although marriage to a female child was still permissible if her father consented, whether she agreed to it or not;^[27] if the father was dead, such consent could be given by her mother, or her brothers, but in this latter case, the girl could annul the marriage when she reached the "standard" age of puberty (12), if she wished.^[27]

The mentally handicapped, and deaf-mutes, were also regarded, by traditional Jewish law, as being unable to give their consent; indeed, marriage to such people was forbidden. However, the rabbis allowed deaf-mutes to marry each other.^[27]